Optimization of cold nitrogen plasma surface modification process for setting up antimicrobial low density polyethylene films

• The optimization of cold nitrogen plasma process parameters for controlled adsorption of Nisin on LDPE polymer was developed.
• The characterization techniques using XPS, ToF-SIMS and surface free energy showed dramatical changes in the surface properties after cold nitrogen plasma treatment.
• The antimicrobial activity was clearly evidenced after Nisin adsorption on the modified LDPE surface.

In order to prevent microbial contamination and food-borne illnesses, antimicrobial active packaging represents an innovative option. The aim of this paper was to optimize the experimental parameters of the plasma treatment. Such pre-treatment can be used to develop an active packaging film by adsorbing a natural antimicrobial peptide “Nisin” on the surface of a commonly used polymer in the agro-food sector “low density polyethylene (LDPE)”. Cold nitrogen (N2) plasma treatment was used to functionalize LDPE and generate a hydrophilic polymer suitable for the adsorption of the peptide. The experimental design technique allowed determining the optimal conditions of the plasma treatment. The lowest contact angle and highest hydrophilic character were obtained for a gas flow rate of 500 cm3/min, a generator power of 300 W and an exposure time of 300 s. The surface characterization techniques X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), contact angle and surface free energy measurements were used to confirm the surface modification after cold plasma treatment. The antimicrobial tests permitted to validate the efficiency of the active packaging films. The plasma treated films showed higher antimicrobial activity after nisin adsorption as compared to the native ones.

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